Zolt Levay

(STScI)

I became intrigued by the Pencil Nebula while reading
David Malin's
magnificent book The Invisible Universe. I have
been astounded by Dr.
Malin's spectacular astronomical photographs for
many years. His work has
set very high technical and aesthetic standards
for astronomical
photography. These images have been a great inspriation
to me personally,
not only to encourage me to pursue astronomy, but
also in my continuing work
to produce images from the Hubble Space Telescope.

Running across the Pencil Nebula, I wondered what
an image made with the
Hubble Space Telescope might show. Hubble's ability
to distinguish fine
details has resulted in some surprises, including
the varied and complex
forms of nebulae. However, it is limited to a field
of view much smaller
than what Dr. Malin's image shows. Nevertheless,
it seemed reasonable to
assume that a Hubble image of the Pencil would show
details not apparent in
images from telescopes on the ground.

The Hubble Heritage Project is fortunate to be
able to use the Hubble Space
Telescope for a limited number of new observations
of our choosing. The
Hubble Heritage Team agreed that the Pencil Nebula
would be a promising
target, likely resulting in a beautiful image. We
decided to use the
recently-installed Advanced Camera for Surveys (ACS)
for the first time for
a Heritage image because of its overall finer resolution
and its greater
sensitivity than the older WFPC2 instrument. We
asked Dr. Bill Blair for his
help in planning our observations because he is
an expert on this type of
object (supernova remnants). In fact, he had some
data on the Pencil,
incluing brightness measurements, which he graciously
shared with us,
confirming that the nebula is quite faint. Nevertheless,
we estimated that
the the time we planned to devote to the observations
would result in
acceptable images.

We reconstructed the colors in this image from
black and white images taken through various filters
to isolate specific colors. We used two types of
filters: reddish and bluish "narrow-band"
filters to isolate light emitted mostly by hydrogen
and oxygen as well as red, yellow-green and blue
"broad-band" filters to render the colors
of the stars fairly accurately. We tried to balance
the contrast and brightness of the various exposures
to show as much detail as possible over the whole
nebula.